382 VIII. CHOLESTEROL AND RELATED STEROLS 



cholesterol, after subcutaneous or intraperitoneal injection of C'''-labeled 

 acetate, or after its injection into the crop gland of hens. 



(5) Primary Products Other Than Acetate 

 Which Are Sources of Cholesterol 



A number of substances which are convertible to acetate can serve as 

 precursors of cholesterol, presumably after conversion to acetate. In ad- 

 dition to these relatively simple molecules, which presumably are con- 

 verted to cholesterol via acetate, more complicated compounds, such as 

 squalene, have like^^^se been showii to be cholesterol precursors. These 

 latter compounds are generally considered to function as intermediates in 

 cholesterol synthesis. 



a. Ethanol. Bloch and Rittenberg^^^ were the first to demonstrate the 

 conversion of ethyl alcohol to cholesterol. In a later study, Curran and 

 Rittenbergi^^ confirmed these results; however, they concluded that etha- 

 nol is not an immediate precursor, but that it must first undergo biologic 

 conversion into acetic acid or into an active acetyl radical before its utiliza- 

 tion for cholesterol synthesis. The liver has been shown to be the organ 

 most active in the metabolism of ethanol. Thus, Masoro and Abramo- 

 witch^^^ reported that rat liver slices convert labeled ethanol to CO2, to 

 fatty acids, and to cholesterol. Although the kidney was shown to sur- 

 pass the liver in its capacity to oxidize alcohol, this organ did not utilize 

 significant amounts of alcohol in the synthesis of fatty acids and of choles- 

 terol. Lung tissue also possesses the capacity to utilize small amounts of 

 alcohol. 



b. Acetone. Smedley-MacLean and Hoffert^^" observed that an alde- 

 hyde is an active metabolite in sterol synthesis. On the other hand, Borek 

 and Rittenberg^^i demonstrated that the ketone, acetone, is converted into 

 cholesterol in the surviving rat liver. It was not certain whether the ace- 

 tone molecule is transformed in toto into cholesterol, or whether only that 

 portion of the molecule which is changed to acetate functions in this man- 

 ner. There is some experimental e\ddence that the latter hypothesis is at 

 least partially correct. A similar transformation of the isopropyl residue 

 of leucine and of isoleucine may account for the demonstration by Bloch 1^- 



187 K. Bloch and D. Rittenberg, /. Biol. Chem., 155, 243-254 (1944). 



188 G. L. Curran and D. Rittenberg, J. Biol. Chem., 190, 17-20 (1951). 



189 E. J. Masoro and H. Abramowitch, Federation Proc, 12, 94 (1953). 

 "« I. Smedley-MacLean and D. Hoffert, Biochem. J., 20, 343-357 (1926). 



191 E. Borek and D. Rittenberg, /. Biol. Chem., 179, 843-845 (1949). 



192 K. Bloch, /. Biol. Chem., 155, 255-263 (1944). 



